Generally, a conventional electro-discharging machine is considered a very slow processing machine; especially, when a working piece has to be processed in several portions, it would take a considerable time to complete the work; occasionally, the delivery time of a product would be delayed. The conventional electro-discharging machine can only process one portion of a work piece at a time; after that portion is completed, the next portion of the work piece will be processed; as a result, time and manpower would be wasted.
Further, the major structure of a conventional electro-discharging machine comprises a movable x-axis and a Y-axis, working racks, and a fixed Z-axis discharging head member; in other words, the machine has only one head member, and therefore the machine requires an excessive period of time to complete a machine operation. Since the working rack can be moved by means of a manual X-axis guide screw rod and a Y-axis guide screw rod, the operation person has difficulty in operating the guide screw rods in the event of a heavy working piece being processed. Also, heavy work pieces can sometimes cause the guide screw rods and the working rack to possibly be deformed; in that case, the precision of the working rack will be jeopardized.
The current patented two-head type of discharging machine is still not deemed a perfect machine because of the drawbacks described as follows:
(1) A discharging machine in U.S. Pat. No. 4,739,145 disclosed by Check et al (145) has a head member to be driven for adjustment with a cylinder along a slide rail. Since the movement range of a mount driven by the cylinder is limited, each head member can only move over one half of the working rack. If the processing portion of a working piece is located within one side of the working rack, the head member which is away from that portion will be unable to move into the area, i.e., the processing space is limited.
(2) In a Japanese Patent JAU 46-16320, the two-head type of electro-discharging machine has a fixed Y-axis to be slid along a sliding rail, being mounted over a processing channel. In case of a large working piece to be processed thereon, it would be rather difficult to place the working piece on the machine; since the movement range of the head members is limited, the processing efficiency would be limited in situations where the surface to be machined is beyond the area that the head member can reach.
(3) In a U.S. Pat. No. 4,670,635 disclosed by Johnson et al, the head member of the machine can be replaced by means of a support arm and a turret. The head member can only be turned at a given angle for Z-axis movement; for movement in other directions, the working rack is the only part that can be moved.